The invention concerns a method and a reactor for the decontamination of ground water in accordance with the generic terms 1 and 6.
Numerous methods for the decontamination of ground water are already known up to the present time.
In the DE 44 25 061 C1 a permeable treatment bed is described for the cleansing of contaminated ground water currents in situ as a ditch erected transversely to the ground water current flow, reaching to a point below the ground water bottom fond, and loaded with filling material removing the ground water contaminating substances or converting in the water. Within and along the ditch, a double-wall permeable for the ground water is envisaged which contains the filling material in its intermediate space. As a result of the length of the cleansing route section within the double wall, there is a more or less adequate contacting time of the ground water with the filling material. The ground water is not selectively but, in its entirety and within the structural-technical measure, is contained, treated and discharged again.
In the DE 42 21 198 C2 a method is described for the removal of water-soluble absorbable pollutants from exiting ground water in the sediments of the surroundings of a contamination source with the help of a narrow wall. In this case, in the way of the exiting ground water a slot is applied which is filled with sorption material. In the way of the exiting ground water, and in the direction of flow downstream of the first slot, a second slot is applied in the sediments and filled with sorption material, as soon as the sorption material in the first slot is loaded up to the level of saturation. This process is continued at random.
In the WO 91/08176 a method is described for the cleansing of ground water contaminated with chlorinated or with halogen-containing organic substances (CKW).
With respect to this, it is proposed that the CKW-contaminated water be channelled for defined holding times through hermetically enclosed metal bodies and that oxygen access be thoroughly avoided in the process. For this purpose it is proposed to excavate a drainage ditch in the water-transporting layer and to locate the metal body in this.
In the DE-A-197 15 038, a description is given for a water-permeable filter wall and a method for making the filter wall to the in-situ ground water cleansing which functions according to the xe2x80x9cfunnel-and-gatexe2x80x9d principle.
The use of the filter wall is bound to certain prerequisites, allowing in particular no consideration of the vertical pollutant distribution and, relevant hereto, the minimization of the water quantities to be cleansed. The use in greater depths is not established. The measure involved here is purely passive.
Furthermore, the problem of cleansing contaminated ground water is also dealt with in the documents U.S. Pat. No. 5,534,154, U.S. Pat. No. 5,487,622 and U.S. Pat. No. 5,362,394.
With all methods known up to the present time, the entire construction-technical contained aquifer areas are treated and again discharged on a broad front. The horizontal current flow calls for a construction width which allows the residence time as required for the degradation of pollutants. Gate, slot or ditch widths are required in sizes of ten meters and more, and these result in high costs.
The invention is therefore based on the task assignment of developing a method and a reactor of the category mentioned at the introduction to this document, with which a cost-favorable and selective ground water extraction from random horizons are ensured for selective and reliable treatment (decontamination).
In accordance with the invention, this task assignment is solved by the features of the claims 1 and 3. According to the invention, the contaminated ground water is directed into a reactor at a random height below the ground water level, and conducted through a reaction chamber with at least one reaction agent in dependence of the required residence duration period, and directed as cleansed ground water at a required height from the reactor, where the height of the input of the ground water into the reactor is selected in accordance with the pollutant type and the pollutant location in the ground water.
For decontamination, the contaminated water flows vertically through a drop shaft designed as a reactor and containing the reactive material.
The reactor according to the invention is located, according to the known drop shaft technology, into a point in the bottom fond of the horizon which conducts the contaminated water.
The reactor has a reaction chamber with at least one feed line and at least one outlet line (gravel casing well, outlet flow wake). The reaction chamber contains at least one reaction agent and reaches up to the reactor base and is closed off below the ground water level.
The coupling of the drop shaft technology with known methods of redevelopment technology provides for hydraulic advantages such as the possibility of the selective ground water extraction from almost random horizons in the required scope. This option is a major advantage for a series of cases of damage. It is frequently the case that contaminations are not evenly distributed in the ground water but are concentrated in certain horizons. For this reason and for decontamination purposes, only this part of the ground water must be extracted and treated. In addition, the treated ground water can be discharged in random depth zones of the aquifer.
In order to cover the scope of pollutants which are heavier than water, and in accordance with an embodiment of the invention, the ground water is conducted to the reactor in the lower zone and discharged as cleansed ground water below the ground water level from the upper zone of the reactor.
In order to cover the scope of pollutants which are lighter than water, oil for example, and in accordance with an embodiment variant of the invention, the ground water is conducted to the reactor in the upper zone below the ground water level and also discharged again after the contaminated ground water, for the purpose of achieving a longer residence duration period in the reactor, was first directed downwards and then upwards along an intermediate wall which is open in the lower zone of the reactor.
In order to cover the scope of pollutants which are in the middle area of the ground water column, for example suspended substances or pollutants in the island areas made from clay/loam for example, and in accordance with a further embodiment of the invention, the ground water is conducted to the reactor in the middle zone and directed along an intermediate wall in a downward direction and, from there, along an intermediate wall into the upper zone of the reactor and withdrawn below the ground water level.
With the previously known xe2x80x9cfunnel-and-gatexe2x80x9d-slot or ditch technology, the entire construction-technical contained aquifer areas are, by contrast, treated and discharged again on a broad front. With the known methods, the horizontal flow current demands a structural width which makes possible the necessary residence time required for pollutant degradation. As the current flow velocity must always be greater than the natural ground water flow velocity and, in the case of complex pollutant mixtures or with substances difficult to metabolize, degradation times of more than ten days are required, gate-, slot- or ditch widths of ten meters and more are required and this leads to an extraordinary cost increase of the construction. The same applies for the depth of the necessary structures. Structures previously realized according to the known methods reach only a few meters in depth. By means of the method according to the invention, vertical flow current lengths (residence times) up to the difference well depthxe2x80x94pressure water level can be realized and pumping would not be necessary in this case. The coverage of larger ground water currents can be achieved by the connection of several wells through non-permeable walls.
Advantageous further developments of the invention result from the subclaims.